virtual prepaid card

Great.

I would appreciate it if you could give me instructions on exactly how to do that?

Of course, you received a physical card, or did you get an e-card?

I received an e-card.  I already activated it.  

When I was with a different internet provider, there was a one-time payment option.  That was how I used a similar card they offered.

I didn't see anything like that in the billing section of the Xfinity site.

Ok, if you have the card info, you should be able to add it to your account as a payment method. Are you not seeing that option?

From our intranet: "To pay, customers should go to the payment section on the Xfinity website or app, select their payment method, and enter the card information."